Electrolytic disposition of chromium



Patented Mar. 19, 1929. 4

UNITED STATES PATENT OFF-ICE.

RUDOLF AUERBACH, OF PROBSTDEUBEN, NEAR LEIPZIG, GERMANY, ASSIGNOR 'I'O GEROMEPLA'IE, INC., OF UNION CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

-ELECTROLYTIC DISPOSITION OF CHROMIU'M.

No Drawing. 7 Application filed January 6, 1927. Serial No. 159,507.

My invention refers to the electrolytic depstances the composition of the solution will osition of metallic chromium, and its partic- Vary from time to time in such manner as to ular object is to provide means whereby such require constant watching and correcting. deposition can be carried through under I have now found that colloidal silicic acid 5 more favorable conditions and in a less exand colloidal silicates are particularly useful pensive manner than was hitherto possible. and eifective in the direction aforementioned.

As is well known to those skilled in the In carrying outmy invention I may, for art, an electrolytically produced deposit of instance, proceed as follows:

chromium will be the denser and the more 10 homogeneous the lower the density of current employed in producing same. If the cur- 5 grams of soluble water glass (N a Si,O,) rent density is too high, exceeding 5 amperes of 28 B. are dissolved in 500 ccms. water, per square decimetre, the electrolytic deposit and tothis solution is added under constant of chromium will be porous and brittle, so stirringa solution of 10- grams chromic acid 65 Example 1. 60

p as to readily splinter oil the base material. in 500 ccms. water. Only after the two solu- Furthermore with such high current .densitions have been mixed in the manner aforeties the separation of the metal willnot occur said, the electrolytic solution is completed by in perfect purity, oxygen compounds being slowly adding further quantities of chromic deposited in the pores which impair the qualacid or chromates and the like. a 70 ities of the deposit. Em Z 2 On the other hand the yield of chromium amp 6 per ampere hour is dependent from the cur- To a solution of 5 grams of soluble Water rent density, this yield increasing as the denglass (N a Si,O,) in 500 ccms. water are sity of current increases. In order, therefore, added under stirring 500 ccms. of a dilute soto obtain as strong a deposit as possible in the lution of a chromium salt, to which has been least possible time, the largest possible denadded sulphuric acid or some other suitable sity of current is preferable. acid. In this manner is obtained a colloidal, have now ascertained that if a. solvatized highly viscous mixture of chromium silicate colloid is added to the solution of chromic acidand silicic acid. 'Also in this case I prefer 30 or cromates employed in the I electrolytic dissolving the rest of the chromium salts process, a homogeneous deposition of chro: only after the colloidal mixture has been finmium will occur over a far wider range of ished. I current densities. In other words, chromium -If strong mineral acids have been used in will be de osited from the solution on the one the production of the silicates, it is preferhand with so low densities of current, that able to subject the solutions to dialysis beunder ordinary conditions no separation of fore preparing themready for use, in order metal would occur. 'On the other hand the to free them from the dispersed particles range within which dense and firmly adherwhich might cause trouble during the electroing deposits are obtained extends up to high lytic process. 0 40 current densities (beyond 15 amperes per I wish it to be understood that I do not desquare decimetre), so that the high yield obsire to be limited to the exact substances and tainable under these conditions,' which operations above described for obvious modiamounts substantially to 30 per cent, can be ficat-ions will occur to a person skilled in the utilized in a commercial manner. art. In view, however, of the fact that most of I claim:

the chromium solutions nowadays in use con- 1. The method of electrolytically dep0sittain either chromic acid or chromates, it is ing metallic chromium, which consists in addimpossible to employ organic colloids. For ing to a solution containing chromic acid, solwhile such colloids will at first act in the manuble freshly made silicic acid and electrolvz- 100 0 .ner above described, nevertheless in conseing the solution. quence of the oxidation of the organic sub- 2. The method of electrolytically depositmg metallic chromium, which consists in adding metallic chromium, which consists in adding about a 1% solution of soluble Waterv ing soluble Water glass (Na si O in about glass (Na Si O to about a 2% solution of a 1% solution to a dilute solution ofa chroohromic acid, mixing the resultant solution mium salt to which has been added an acid 5 With further quantities of a, chromic acid and and electrolyzing the solution.

electrolyzing the solution. In testimony whereof I affix my signature.

3. The method of electrolytically deposit- RUDOLF AUERBACH. 

